--- 1/draft-ietf-rmcat-coupled-cc-07.txt 2019-01-10 05:13:17.925381962 -0800 +++ 2/draft-ietf-rmcat-coupled-cc-08.txt 2019-01-10 05:13:17.981383306 -0800 @@ -1,19 +1,19 @@ RTP Media Congestion Avoidance Techniques (rmcat) S. Islam Internet-Draft M. Welzl Intended status: Experimental S. Gjessing -Expires: March 19, 2018 University of Oslo - September 15, 2017 +Expires: July 14, 2019 University of Oslo + January 10, 2019 Coupled congestion control for RTP media - draft-ietf-rmcat-coupled-cc-07 + draft-ietf-rmcat-coupled-cc-08 Abstract When multiple congestion controlled Real-time Transport Protocol (RTP) sessions traverse the same network bottleneck, combining their controls can improve the total on-the-wire behavior in terms of delay, loss and fairness. This document describes such a method for flows that have the same sender, in a way that is as flexible and simple as possible while minimizing the amount of changes needed to existing RTP applications. It specifies how to apply the method for @@ -22,86 +22,87 @@ congestion control algorithms. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- - Drafts is at http://datatracker.ietf.org/drafts/current/. + Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on March 19, 2018. + This Internet-Draft will expire on July 14, 2019. Copyright Notice - Copyright (c) 2017 IETF Trust and the persons identified as the + Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents - (http://trustee.ietf.org/license-info) in effect on the date of + (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Architectural overview . . . . . . . . . . . . . . . . . . . 5 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . 9 - 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 10 + 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 11 6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 11 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 6.2. General recommendations . . . . . . . . . . . . . . . . . 11 + 6.2. General recommendations . . . . . . . . . . . . . . . . . 12 7. Expected feedback from experiments . . . . . . . . . . . . . 12 - 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 + 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 - 11.1. Normative References . . . . . . . . . . . . . . . . . . 13 + 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 + 11.1. Normative References . . . . . . . . . . . . . . . . . . 14 11.2. Informative References . . . . . . . . . . . . . . . . . 14 - Appendix A. Application to GCC . . . . . . . . . . . . . . . . . 15 + Appendix A. Application to GCC . . . . . . . . . . . . . . . . . 16 Appendix B. Scheduling . . . . . . . . . . . . . . . . . . . . . 16 Appendix C. Example algorithm - Passive FSE . . . . . . . . . . 16 C.1. Example operation (passive) . . . . . . . . . . . . . . . 19 Appendix D. Change log . . . . . . . . . . . . . . . . . . . . . 23 D.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . 23 D.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 23 D.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 23 D.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 23 D.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 24 D.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 24 D.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 24 D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . 24 D.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 24 D.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 24 D.2.4. Changes from -02 to -03 . . . . . . . . . . . . . . . 24 - D.2.5. Changes from -03 to -04 . . . . . . . . . . . . . . . 24 + D.2.5. Changes from -03 to -04 . . . . . . . . . . . . . . . 25 D.2.6. Changes from -04 to -05 . . . . . . . . . . . . . . . 25 D.2.7. Changes from -05 to -06 . . . . . . . . . . . . . . . 25 D.2.8. Changes from -06 to -07 . . . . . . . . . . . . . . . 25 + D.2.9. Changes from -07 to -08 . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 1. Introduction When there is enough data to send, a congestion controller attempts to increase its sending rate until the path's capacity has been reached. Some controllers detect path capacity by increasing the sending rate further, until packets are ECN-marked [RFC8087] or dropped, and then decreasing the sending rate until that stops happening. This process inevitably creates undesirable queuing delay @@ -161,24 +161,24 @@ Shared Bottleneck Detection (SBD): The entity that determines which flows traverse the same bottleneck in the network, or the process of doing so. 3. Limitations Sender-side only: Shared bottlenecks can exist when multiple flows originate from the same sender, or when flows from different senders reach the - same receiver (see [I-D.ietf-rmcat-sbd], section 3). Coupled - congestion control as described here only supports the former - case, not the latter, as it operates inside a single host on - the sender side. + same receiver (see [RFC8382], section 3). Coupled congestion + control as described here only supports the former case, not + the latter, as it operates inside a single host on the sender + side. Shared bottlenecks do not change quickly: As per the definition above, a bottleneck depends on cross traffic, and since such traffic can heavily fluctuate, bottlenecks can change at a high frequency (e.g., there can be oscillation between two or more links). This means that, when flows are partially routed along different paths, they may quickly change between sharing and not sharing a bottleneck. For simplicity, here it is assumed that a shared bottleneck is valid for a time interval that is significantly longer than the @@ -289,48 +289,55 @@ 2. Via configuration: e.g. by assuming that a common wireless uplink is also a shared bottleneck. 3. From measurements: e.g. by considering correlations among measured delay and loss as an indication of a shared bottleneck. The methods above have some essential trade-offs: e.g., multiplexing is a completely reliable measure, however it is limited in scope to two end points (i.e., it cannot be applied to couple congestion controllers of one sender talking to multiple receivers). A - measurement-based SBD mechanism is described in [I-D.ietf-rmcat-sbd]. + measurement-based SBD mechanism is described in [RFC8382]. Measurements can never be 100% reliable, in particular because they are based on the past but applying coupled congestion control means to make an assumption about the future; it is therefore recommended to implement cautionary measures, e.g. by disabling coupled congestion control if enabling it causes a significant increase in delay and/or packet loss. Measurements also take time, which entails - a certain delay for turning on coupling (refer to - [I-D.ietf-rmcat-sbd] for details). Using system configuration to - decide about shared bottlenecks can be more efficient (faster to - obtain) than using measurements, but it relies on assumptions about - the network environment. + a certain delay for turning on coupling (refer to [RFC8382] for + details). Using system configuration to decide about shared + bottlenecks can be more efficient (faster to obtain) than using + measurements, but it relies on assumptions about the network + environment. 5.2. FSE The FSE contains a list of all flows that have registered with it. For each flow, it stores the following: o a unique flow number f to identify the flow. o the FGI of the FG that it belongs to (based on the definitions in this document, a flow has only one bottleneck, and can therefore be in only one FG). o a priority P(f), which is a positive number, greater than zero. o The rate used by the flow in bits per second, FSE_R(f). + o The desired rate DR(f) of flow f. This can be smaller than + FSE_R(f) if the application feeding into the flow has less data to + send than FSE_R(f) would allow, or if a maximum value is imposed + on the rate. In the absence of such limits DR(f) must be set to + the sending rate provided by the congestion control module of flow + f. + Note that the absolute range of priorities does not matter: the algorithm works with a flow's priority portion of the sum of all priority values. For example, if there are two flows, flow 1 with priority 1 and flow 2 with priority 2, the sum of the priorities is 3. Then, flow 1 will be assigned 1/3 of the aggregate sending rate and flow 2 will be assigned 2/3 of the aggregate sending rate. Priorities can be mapped to the "very-low", "low", "medium" or "high" priority levels described in [I-D.ietf-rtcweb-transports] by simply using the values 1, 2, 4 and 8, respectively. @@ -356,131 +363,143 @@ Below, two example algorithms are described. While other algorithms could be used instead, the same algorithm must be applied to all flows. Names of variables used in the algorithms are explained below. o CC_R(f) - The rate received from the congestion controller of flow f when it calls UPDATE. o FSE_R(f) - The rate calculated by the FSE for flow f. + o DR(f) - The desired rate of flow f. + o S_CR - The sum of the calculated rates of all flows in the same FG; this value is used to calculate the sending rate. o FG - A group of flows having the same FGI, and hence sharing the same bottleneck. o P(f) - The priority of flow f which is received from the flow's congestion controller; the FSE uses this variable for calculating FSE_R(f). o S_P - The sum of all the priorities. + o TLO - The total leftover rate: the sum of rates that could not be + assigned to flows that were limited by their desired rate. + + o S_P2 - The sum of all the priorities of flows to which a share of + the TLO can be assigned. + 5.3.1. Example algorithm 1 - Active FSE This algorithm was designed to be the simplest possible method to assign rates according to the priorities of flows. Simulations results in [fse] indicate that it does however not significantly reduce queuing delay and packet loss. (1) When a flow f starts, it registers itself with SBD and the FSE. FSE_R(f) is initialized with the congestion controller's initial rate. SBD will assign the correct FGI. When a flow is assigned an FGI, it adds its FSE_R(f) to S_CR. (2) When a flow f stops or pauses, its entry is removed from the list. (3) Every time the congestion controller of the flow f determines a new sending rate CC_R(f), the flow calls UPDATE, which carries out the tasks listed below to derive the new sending rates for - all the flows in the FG. A flow's UPDATE function uses a local - (i.e. per-flow) temporary variable S_P, which is the sum of all - the priorities. + all the flows in the FG. A flow's UPDATE function uses three + local (i.e. per-flow) temporary variables: S_P, TLO and S_P2. (a) It updates S_CR. S_CR = S_CR + CC_R(f) - FSE_R(f) (b) It calculates the sum of all the priorities, S_P. S_P = 0 for all flows i in FG do S_P = S_P + P(i) end for - (c) It calculates the sending rates for all the flows in an FG - and distributes them. + (c) It calculates the sending rates for all the flows in an FG, + the total leftover rate (TLO) from flows that are limited + by their desired rate, and the sum of the priorities of all + other flows, S_P2. + TLO = 0 + S_P2 = 0 for all flows i in FG do - FSE_R(i) = (P(i)*S_CR)/S_P + FSE_R(i) = P(i) * S_CR /S_P + if FSE_R(i) >= DR(i) then + TLO = TLO + FSE_R(i) - DR(i) + FSE_R(i) = DR(i) + else + S_P2 = S_P2 + P(i) + end if + end for + + (d) It checks if there are flows that are limited by their DR + and cannot accept their share of the TLO, and updates TLO + and S_P2 accordingly. + + for all flows i in FG do + if FSE_R(i) < DR(i) then + if FSE_R(i) + TLO * P(i) / S_P2 > DR(i) then + TLO = TLO - ( DR(i) - FSE_R(i) ) + FSE_R(i) = DR(i) + S_P2 = S_P2 - P(i) + end if + end if + end for + + (e) It assigns the non-limited flow their share of the total + leftover rate and sends all the rates to all the flows. + + for all flows i in FG do + if FSE_R(i) < DR(i) then + FSE_R(i) = FSE_R(i) + P(i) * TLO / S_P2 + end if send FSE_R(i) to the flow i end for 5.3.2. Example algorithm 2 - Conservative Active FSE - This algorithm extends algorithm 1 to conservatively emulate the + This algorithm changes algorithm 1 to conservatively emulate the behavior of a single flow by proportionally reducing the aggregate rate on congestion. Simulations results in [fse] indicate that it can significantly reduce queuing delay and packet loss. - (1) When a flow f starts, it registers itself with SBD and the FSE. - FSE_R(f) is initialized with the congestion controller's initial - rate. SBD will assign the correct FGI. When a flow is assigned - an FGI, it adds its FSE_R(f) to S_CR. - - (2) When a flow f stops or pauses, its entry is removed from the - list. - - (3) Every time the congestion controller of the flow f determines a - new sending rate CC_R(f), the flow calls UPDATE, which carries - out the tasks listed below to derive the new sending rates for - all the flows in the FG. A flow's UPDATE function uses a local - (i.e. per-flow) temporary variable S_P, which is the sum of all - the priorities, and a local variable DELTA, which is used to - calculate the difference between CC_R(f) and the previously - stored FSE_R(f). To prevent flows from either ignoring - congestion or overreacting, a timer keeps them from changing - their rates immediately after the common rate reduction that - follows a congestion event. This timer is set to 2 RTTs of the - flow that experienced congestion because it is assumed that a - congestion event can persist for up to one RTT of that flow, - with another RTT added to compensate for fluctuations in the + Step (a) of the UPDATE function is changed as described below. This + also introduces a local variable DELTA, which is used to calculate + the difference between CC_R(f) and the previously stored FSE_R(f). + To prevent flows from either ignoring congestion or overreacting, a + timer keeps them from changing their rates immediately after the + common rate reduction that follows a congestion event. This timer is + set to 2 RTTs of the flow that experienced congestion because it is + assumed that a congestion event can persist for up to one RTT of that + flow, with another RTT added to compensate for fluctuations in the measured RTT value. (a) It updates S_CR based on DELTA. - if Timer has expired or not set then + if Timer has expired or was not set then DELTA = CC_R(f) - FSE_R(f) if DELTA < 0 then // Reduce S_CR proportionally S_CR = S_CR * CC_R(f) / FSE_R(f) Set Timer for 2 RTTs else S_CR = S_CR + DELTA end if end if - (b) It calculates the sum of all the priorities, S_P. - - S_P = 0 - for all flows i in FG do - S_P = S_P + P(i) - end for - - (c) It calculates the sending rates for all the flows in an FG - and distributes them. - - for all flows i in FG do - FSE_R(i) = (P(i)*S_CR)/S_P - send FSE_R(i) to the flow i - end for - 6. Application This section specifies how the FSE can be applied to specific congestion control mechanisms and makes general recommendations that facilitate applying the FSE to future congestion controls. 6.1. NADA Network-Assisted Dynamic Adapation (NADA) [I-D.ietf-rmcat-nada] is a congestion control scheme for rtcweb. It calculates a reference rate @@ -540,21 +560,23 @@ testers are invited to document their findings in an Internet draft. 8. Acknowledgements This document has benefitted from discussions with and feedback from Andreas Petlund, Anna Brunstrom, Colin Perkins, David Hayes, David Ros (who also gave the FSE its name), Ingemar Johansson, Karen Nielsen, Kristian Hiorth, Mirja Kuehlewind, Martin Stiemerling, Spencer Dawkins, Varun Singh, Xiaoqing Zhu, and Zaheduzzaman Sarker. The authors would like to especially thank Xiaoqing Zhu and Stefan - Holmer for helping with NADA and GCC. + Holmer for helping with NADA and GCC, and Julius Flohr for helping us + correct the active algorithm for the case of application-limited + flows. This work was partially funded by the European Community under its Seventh Framework Programme through the Reducing Internet Transport Latency (RITE) project (ICT-317700). 9. IANA Considerations This memo includes no request to IANA. 10. Security Considerations @@ -581,37 +603,37 @@ eliminated, and no major harm is done. Implementers should also be aware of the Security Considerations sections of [RFC3124], [RFC5348], and [RFC7478]. 11. References 11.1. Normative References [I-D.ietf-rmcat-nada] - Zhu, X., Pan, R., Ramalho, M., Cruz, S., Jones, P., Fu, - J., and S. D'Aronco, "NADA: A Unified Congestion Control - Scheme for Real-Time Media", draft-ietf-rmcat-nada-04 - (work in progress), March 2017. + Zhu, X., *, R., Ramalho, M., Cruz, S., Jones, P., Fu, J., + and S. D'Aronco, "NADA: A Unified Congestion Control + Scheme for Real-Time Media", draft-ietf-rmcat-nada-09 + (work in progress), August 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ - RFC2119, March 1997, . + Requirement Levels", BCP 14, RFC 2119, + DOI 10.17487/RFC2119, March 1997, + . [RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager", RFC 3124, DOI 10.17487/RFC3124, June 2001, . [RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP - Friendly Rate Control (TFRC): Protocol Specification", RFC - 5348, DOI 10.17487/RFC5348, September 2008, + Friendly Rate Control (TFRC): Protocol Specification", + RFC 5348, DOI 10.17487/RFC5348, September 2008, . 11.2. Informative References [anrw2016] Islam, S. and M. Welzl, "Start Me Up:Determining and Sharing TCP's Initial Congestion Window", ACM, IRTF, ISOC Applied Networking Research Workshop 2016 (ANRW 2016) , 2016. @@ -624,66 +646,65 @@ 2014. [fse-noms] Islam, S., Welzl, M., Hayes, D., and S. Gjessing, "Managing Real-Time Media Flows through a Flow State Exchange", IEEE NOMS 2016, Istanbul, Turkey , 2016. [I-D.ietf-rmcat-eval-test] Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test Cases for Evaluating RMCAT Proposals", draft-ietf-rmcat- - eval-test-05 (work in progress), April 2017. + eval-test-08 (work in progress), November 2018. [I-D.ietf-rmcat-gcc] Holmer, S., Lundin, H., Carlucci, G., Cicco, L., and S. Mascolo, "A Google Congestion Control Algorithm for Real- Time Communication", draft-ietf-rmcat-gcc-02 (work in progress), July 2016. - [I-D.ietf-rmcat-sbd] - Hayes, D., Ferlin, S., Welzl, M., and K. Hiorth, "Shared - Bottleneck Detection for Coupled Congestion Control for - RTP Media.", draft-ietf-rmcat-sbd-08 (work in progress), - July 2017. - [I-D.ietf-rtcweb-overview] Alvestrand, H., "Overview: Real Time Protocols for - Browser-based Applications", draft-ietf-rtcweb-overview-18 - (work in progress), March 2017. + Browser-based Applications", draft-ietf-rtcweb-overview-19 + (work in progress), November 2017. [I-D.ietf-rtcweb-transports] Alvestrand, H., "Transports for WebRTC", Internet-draft draft-ietf-rtcweb-transports-17.txt, October 2016. [IETF-93] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled Congestion Control for RTP Media", July 2015, . [IETF-94] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled Congestion Control for RTP Media", November 2015, . [RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- Time Communication Use Cases and Requirements", RFC 7478, - DOI 10.17487/RFC7478, March 2015, . + DOI 10.17487/RFC7478, March 2015, + . [RFC7656] Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms for Real-Time Transport Protocol (RTP) Sources", RFC 7656, - DOI 10.17487/RFC7656, November 2015, . + DOI 10.17487/RFC7656, November 2015, + . [RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using - Explicit Congestion Notification (ECN)", RFC 8087, DOI - 10.17487/RFC8087, March 2017, . + Explicit Congestion Notification (ECN)", RFC 8087, + DOI 10.17487/RFC8087, March 2017, + . + + [RFC8382] Hayes, D., Ed., Ferlin, S., Welzl, M., and K. Hiorth, + "Shared Bottleneck Detection for Coupled Congestion + Control for RTP Media", RFC 8382, DOI 10.17487/RFC8382, + June 2018, . [rtcweb-rtp-usage] Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time Communication (WebRTC): Media Transport and Use of RTP", Internet-draft draft-ietf-rtcweb-rtp-usage-26.txt, March 2016. [transport-multiplex] Westerlund, M. and C. Perkins, "Multiple RTP Sessions on a Single Lower-Layer Transport", Internet-draft draft- @@ -727,35 +748,24 @@ update and react to the overall FSE state more often than longer-RTT flows, which can produce unwanted side effects. This problem is more significant when the congestion control convergence depends on the RTT. While the passive algorithm works better for congestion controls with RTT-independent convergence, it can still produce oscillations on short time scales. The algorithm described below is therefore considered as highly experimental and not safe to deploy outside of testbed environments. Results of a simplified passive FSE algorithm with both NADA and GCC can be found in [fse-noms]. - This passive version of the FSE stores the following information in - addition to the variables described in Section 5.2: - - o The desired rate DR(f) of flow f. This can be smaller than the - calculated rate if the application feeding into the flow has less - data to send than the congestion controller would allow. In case - of a bulk transfer, DR(f) must be set to CC_R(f) received from the - congestion module of flow f. - - The passive version of the FSE contains one static variable per FG - called TLO (Total Leftover Rate -- used to let a flow 'take' - bandwidth from application-limited or terminated flows) which is - initialized to 0. For the passive version, S_CR is limited to - increase or decrease as conservatively as a flow's congestion - controller decides in order to prohibit sudden rate jumps. + In the passive version of the FSE, TLO (the Total Leftover Rate) is a + static variable per FG which is initialized to 0. Additionally, S_CR + is limited to increase or decrease as conservatively as a flow's + congestion controller decides in order to prohibit sudden rate jumps. (1) When a flow f starts, it registers itself with SBD and the FSE. FSE_R(f) and DR(f) are initialized with the congestion controller's initial rate. SBD will assign the correct FGI. When a flow is assigned an FGI, it adds its FSE_R(f) to S_CR. (2) When a flow f stops or pauses, it sets its DR(f) to 0 and sets P(f) to -1. (3) Every time the congestion controller of the flow f determines a @@ -1094,20 +1104,26 @@ coupling algorithm. D.2.7. Changes from -05 to -06 o Incorporated comments by Colin Perkins. D.2.8. Changes from -06 to -07 o Addressed OPSDIR, SECDIR, GENART, AD and IESG comments. +D.2.9. Changes from -07 to -08 + + o Updated the algorithms in section 5 to support application-limited + flows. Moved definition of Desired Rate from appendix to section + 5. Updated references. + Authors' Addresses Safiqul Islam University of Oslo PO Box 1080 Blindern Oslo N-0316 Norway Phone: +47 22 84 08 37 Email: safiquli@ifi.uio.no